The new UI seems to escape URLs differently than the old. E.g., consider the following query: (project:mediawiki/skins/MinervaNeue+OR+project:mediawiki/extensions/MobileFrontend). The URL in the old UI is this:
The new UI shows a 404. I can, however, rebuild the query in the new UI and it generates this less friendly URL:
The old UI works with the new URLs but the new UI doesn't work with the old URLs. It's probably not a big deal since I can just make new URLs but it's confusing. I thought these queries were completely unsupported until I tried to file this report. Also, the old URLs are so easy to construct by hand and read.
Another longer example:
And the new query: